Multi-track analog optical sensing system and method

Abstract

An optical sensor and an optical sensing system and method in which both analog and digital techniques are employed. The sensor comprises an encoder and an illumination source. The encoder includes a plurality of tracks, and the illumination source illuminates each track with an associated optical input signal. Each input signal comprises light in a wavelength range different from the wavelength ranges of the other input signals. Each track includes means responsive to the value of a measurand for modulating the intensity of the associated input signal, in one of N different ways, to produce a corresponding modulated signal, N being greater than 2. The intensities of the modulated signals thereby encode the value of the measurand. The illumination source may also produce a reference signal that is not modulated by the measurand. The modulated and referenced signal may be combined into an output signal, and the composite input signal and output signals may be conveyed to and from the sensor via fiber-optic cables.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. A sensor for use in an optical sensing system for determining a value of a measurand, the sensor comprising: encoding means having a plurality of tracks;   illumination means for illuminating each track with an associated optical input signal, each input signal comprising light in a wavelength range different from the wavelength ranges of the other input signals; and   each track including means responsive to the value of the measurand for modulating the intensity of the associated input signal in one of N different ways to produce a corresponding modulated signal, N being greater than 2, whereby the intensities of the modulated signals encode the value of the measurand.   
     
     
       2. The sensor of claim 1, wherein the illumination means comprises means for receiving a composite input signal comprising light in each wavelength range, and means for demultiplexing the composite input signal to produce the respective optical input signals. 
     
     
       3. The sensor of claim 2, wherein the means for demultiplexing comprises a filter associated with each track, each filter including means for receiving a portion of the composite input signal and for preferentially selecting wavelength components in the associated wavelength range to form the input signal for the track. 
     
     
       4. The sensor of claim 3, wherein the filters form a linear array adjacent to the tracks, and wherein the means for demultiplexing comprises means for receiving the composite input signal and for forming the composite input signal into a linear beam that strikes the array. 
     
     
       5. The sensor of claim 2, wherein the means for demultiplexing comprises a prism for dispersing the composite input signal to produce the optical input signals. 
     
     
       6. The sensor of claim 2, wherein the means for demultiplexing comprises a diffraction grating for dispersing the composite input signal to produce the optical input signals. 
     
     
       7. The sensor of claim 1, further comprising means for combining the modulated signals to produce an output signal, whereby the intensity of light in the output signal in the respective wavelength ranges encodes the value of the measurand. 
     
     
       8. The sensor of claim 7, wherein the illumination means includes means for producing a reference signal comprising light in a reference wavelength range different from the wavelength ranges of the input signals, and wherein the means for combining includes means for combining the reference signal with the modulated signals to produce the output signal. 
     
     
       9. The sensor of claim 8, wherein the illumination means comprises means for receiving a composite input signal comprising light in each wavelength range including the reference wavelength range, and means for demultiplexing the composite input signal to produce the respective input signals and the reference signal. 
     
     
       10. The sensor of claim 1, wherein each track comprises a plurality of modulation elements, each modulation element comprising means for modulating the intensity of the associated input signal in one of the N ways. 
     
     
       11. The sensor of claim 10, wherein at least one of the modulation elements comprises a pattern of nontransmitting areas. 
     
     
       12. The sensor of claim 10, wherein at least N-1 modulation elements comprise a single nontransmitting area having a variable size. 
     
     
       13. The sensor of claim 10, wherein at least one of the modulation elements comprises a pattern of reflecting areas. 
     
     
       14. The sensing system of claim 1, wherein the measurand is the position of a movable member, wherein the encoder is coupled to the movable member such that the encoder moves when the movable member moves. 
     
     
       15. An optical sensing system for determining a value of a measurand, the system comprising: a source for producing a composite input signal comprising light in a plurality of different wavelength ranges;   a sensor comprising encoding means having a plurality of tracks, illumination means for receiving the composite input signal and for demultiplexing the composite input signal to produce an optical input signal associated with each track, each input signal comprising light in one of the wavelength ranges different from the wavelength ranges of the other input signals, each track including means responsive to the value of the measurand for modulating the intensity of the associated input signal in one of N different ways to produce a corresponding modulated signal, N being greater than 2, the sensor further comprising combining means for combining the modulated signals to produce an output signal, whereby the intensity of light in the output signal in the respective wavelength ranges encodes the value of the measurand;   a detector for detecting the intensity of light in each of the wavelength ranges in the output signal to thereby determine the value of the measurand; and   fiber-optic cable means for conveying the composite input signal from the source to the sensor and for conveying the output signal from the sensor to the detector.   
     
     
       16. The system of claim 15, wherein the illumination means also produces an optical reference signal comprising light in one of the wavelength ranges different from the wavelength ranges of the input signals, wherein the combining means combines the reference signal with the modulated signals to produce the output signal, and wherein the detector compares the intensity of light in each of the wavelength ranges associated with one of the input signals to the intensity of light in the wavelength range associated with the reference signal, to determine the modulation level produced by the track. 
     
     
       17. The system of claim 15, wherein each track comprises a plurality of modulation elements, each modulation element comprising means for modulating the intensity of the associated input signal in one of the N ways. 
     
     
       18. The system of claim 17, wherein at least one of the modulation elements comprises a pattern of nontransmitting areas. 
     
     
       19. The system of claim 17, wherein at least N-1 modulation elements comprise a single nontransmitting area having a variable size. 
     
     
       20. The system of claim 17, wherein at least one of the modulation elements comprises a pattern of reflecting areas. 
     
     
       21. The system of claim 15, wherein the illumination means comprises a filter associated with each track, each filter including means for receiving a portion of the composite input signal and for preferentially selecting wavelength components in the associated wavelength range to form the input signal for the track. 
     
     
       22. The system of claim 21, wherein the filters form a linear array adjacent to the tracks, and wherein the illumination means comprises means for receiving the composite input signal and for forming the composite input signal into a linear beam that strikes the array. 
     
     
       23. The system of claim 15, wherein the measurand is the position of a movable member, and wherein the encoder is coupled to the movable member such that the encoder moves when the movable member moves. 
     
     
       24. An optical method for determining a value of a mearsurand, the method comprising: providing encoding means having a plurality of tracks, each track including means responsive to the value of the measurand for modulating the intensity of an associated input signal in one of N different ways to produce a corresponding modulated signal, N being greater than two;   producing a composite input signal comprising light in a plurality of different wavelength ranges and transmitting the composite input signal to the encoding means;   demultiplexing the composite input signal to produce an optical input signal associated with each track, each input signal comprising light in one of the wavelength ranges different from the wavelength ranges of the other input signals;   combining the modulated signals to produce an output signal, whereby the intensity of light in each of the wavelength ranges in the output signal encodes the value of the measurand.   
     
     
       25. The method of claim 24, wherein the composite input signal comprises light in a referenced wavelength range different from the wavelength ranges of the input signals, wherein the demultiplexing step demultiplexes the composite input signal to produce the optical input signals and an optical reference signal comprising light in the referenced wavelength range, and wherein the combining step includes combining the reference signal with the modulated signals to produce the output signal. 
     
     
       26. An optical sensing system for determining a value of a measurand, the system comprising: a source for producing a composite input signal comprising light in a plurality of different wavelength ranges;   a sensor comprising encoding means having a plurality of tracks, illumination means for receiving the composite input signal and for demultiplexing the composite input signal to produce an optical input signal associated with each track, each input signal comprising light in one of the wavelength ranges different from the wavelength ranges of the other input signals, each track including means reponsive to the value of the measurand for modulating the intensity of the associated input signal to produce a corresponding modulated signal, the sensor further comprising combining means for combining the modulated signals to produce an output signal, whereby the intensity of light in the output signal in the respective wavelength ranges encodes the value of the measurand;   a detector for detecting the intensity of light in each of the wavelength ranges in the output signal to thereby determine the value of the measurand, the detector including means for assigning the intensity to one of N different levels, N being greater than 2; and   fiber-optic cable means for conveying the composite input signal from the source to the sensor and for conveying the output signal from the sensor to the detector.